Douglas Davidson

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An integrated model stream ecosystem fate and effect study of dodecyl linear alkylbenzene sulfonate (C(12)LAS) was performed in the summer and fall of 1996. The study addressed responses of periphytic microbes, immature benthic fauna including abundance, drift, and emergence of adult insects in a 56-day exposure. Exposures ranged from 126 to 2978 microg/L(More)
The relative assimilation efficiencies of two common British species of slug, Limax flavus (L.) and Arion hortensis (Fér.), were studied in the laboratory using a gravimetric method. Results are given for adult slugs feeding on carrot root and potato tuber at 5°, 10°, 15°, and 20° C, and for L. flavus juveniles of known age feeding on potato at 10° and 15°(More)
Developing lateral roots of V. faba were treated with 5-aminouracil for up to 6 hours using the 5-AU inhibition method discussed in this paper; the duration of G2+mitosis/2 and the percentages of slow dividing cells were estimated from the fall in MI observed in just emerged meristems, very large primordia and large primordia. The results indicate that(More)
Treatment of Vicia faba lateral roots with a range of concentrations of 5-aminouracil (5-AU) indicate that cells are stopped at a particular point in interphase . The timing of the fall in mitotic index suggests that cells are held at the S G2 transition . When cells are held at this point, treatments with 5-AU can be used to estimate the duration of G 2 +(More)
Following neurulation, the frog segments c.40 somites and concurrently undergoes a striking elongation along the anteroposterior axis. This elongation (excluding the head) is largely the result of a presegmental extension of posterior tissue with a lesser contribution from the extension of segmented tissue. Presegmental extension is entirely the result of(More)
Treatments with tritiated thymidine (TdR-(3)H) have revealed the existence of two populations of mitotically active cells in meristems of lateral roots of Vicia faba. A rapidly dividing population, with a cycle time of 14 hr, constitutes about half the cells in the meristem. A second population of cells, with a cycle time in excess of 30 hr, is also(More)
Treatment of Vicia faba lateral roots with a range of concentrations of 5-aminouracil (5-AU) indicate that cells are stopped at a particular point in interphase. The timing of the fall in mitotic index suggests that cells are held at the S - G(2) transition. When cells are held at this point, treatments with 5-AU can be used to estimate the duration of G(2)(More)
1. Mitoses were seen 2 to 10 days after X irradiation or colchicine treatment, an observation indicating that cell division does occur in roots whose growth in length has been temporarily inhibited. The cessation of growth cannot, therefore, be ascribed to the inhibition of mitosis. 2. The relative frequencies, after irradiation, of cells with dicentric(More)
The effects of continuous exposure to C12-alkyl sulfate on a periphytic microbial community were determined in an 8-week stream mesocosm study. C12-alkyl sulfate concentrations ranged from environmentally relevant (< 10-20 micrograms/liter) to unrealistically high concentrations (> 1500 micrograms/liter). Endpoints evaluated included turnover rates,(More)